Here is the trick to open multiple yahoo...
Yahoo Messenger trick-How to open Multiple Yahoo Messenger???
1. Go to start > Run > Type regedit > Press Enter
2. Click on the plus sign near the folder HKEY_CURRENT_USER
3. Click on the plus sign near the folder Software
4. Click on the plus sign near the folder Yahoo
5. Click on the plus sign near the folder Pager
6. Right Click on the folder name Test > New > DWORD Value
7. Right side you will get a file named New Value #1
8. Right Click on the file New Value #1 and Rename it as “Plural” and press enter
9. Double Click on the file Plural
10. You will get a window named Edit DWORD Value
11. Type 1 inside 'Select the Value data' and press enter
12. Close the registry editor window
13. Now you can launch multiple windows and use different ID's